1. Field of the Invention
The present invention refers to a cutter of a boring head.
This invention deals with cutters both for tunnel boring heads and raise boring heads.
2. Description of Related Art
Prior art roller bearings for cutters of tunnel boring heads, see e.g. U.S. Pat. No. 4,784,438, have usually tapered rollers that are located between an inner and an outer race of the bearing. The circumferential distance between the tapered rollers is controlled by a cage that also is located between the inner and outer races. Since the inner race is stationary, i.e. not rotatable relative to the shaft, said inner race will be subjected to high stresses within a very limited area of its circumference. This means that the inner race will be damaged relatively soon compared to the outer race that rotates relative to the inner race and thus is worn evenly. The consequence of this is that it is favourable to have the inner race as a separate element that is exchangeable when the inner race is worn out. However, there is no need to have the outer race as a separate element since the outer race will normally last for the entire life of the cutter.
The same type of roller bearing is also knowh for raise boring cutters, see e.g. U.S. Pat. No. 4,509,607. In principle the same disadvantages apply as in a cutter or tunnel boring.